Relaxation oscillator



May 15, 1951 w. H. BLISS 5 RELAXATION OSCILLATOR Filed Feb. 28, 1946 I 2SheetsShee l INVENTOR WAQREN H. @MSS ATTORN EY May 15, 1951 w. H. BLISSRELAXATION OSCILLATOR 2 Sheets-Sheet 2 Filed Feb. 28, 1946 INVENTORARREN H uss ATTO R N EY Patented May 15, 1951 RELAXATION OSCILLATORWarren H. Bliss, Riverhead, N. Y., assignor to Radio Corporation ofAmerica, a corporation of Delaware Application February 28, 1946, SerialNo. 650,956

Claims.

This invention relates to relaxation oscillators. It deals with a typeof oscillator wherein a resonant tank circuit is coupled to anelectronic circuit arrangement in such manner that the pulses of energynecessary to maintain oscillations in the tank circuit are derived fromtwo discharge devices which have a flip-flop action. The flip-flopaction is in turn synchronized from the sine wave of the tank circuit.

Accordingly it is an object of my invention to provide a relaxationoscillator of novel type which is capable of sustaining oscillations byitself but which is maintained stable in frequency by the aid of afrequency controlling tank circuit or the equivalent thereof.

It is another object of my invention to provide a relaxation oscillatorthe frequency of which is to be maintained constant by means of aresonant circuit coupled thereto, said resonant circuit being energizedfrom the output of the relaxation oscillator proper.

In the performance of a relaxation oscillator such as herein disclosed asimilarity will be observed to that of a spring driven clock movement incombination with a swinging pendulum. The pendulum controls the rate, ortiming of the clock movement.

My invention will now be described in more detail reference being madeto the accompanyin drawing in which:

Fig. 1 shows a preferred embodiment; Figs. 2 and 3 illustrate modifiedversions; and Fig. 4 shows a series of curves representing generatedwave shapes.

Referring first to Fig. 1 I show therein a resonant tank circuitcomprising inductance I in parallel with a capacitor 2. This combinationis connected between ground and the control grid of a triode tube 4. Thecathodes of tube 4 and of a second tube H3 are interconnected and arenormally connected to ground through an adjustable resistor 9. Thisresistor, however, may be at times shunted by a circuit of relativelylow resistance comprising a starting resistor 24 in series with astarting switch 23. The switch 23 is used for starting the oscillatorycondition in the circuit. A peculiarity of this circuit arrangement isthat resistor 9 is preferably chosen to have a relatively high ohmicvalue, so that the relaxation oscillator is not self-starting.

Energizing potential from a D. C. source indicated as B+ (and having agrounded negative terminal) is shown connected to the anodes of the twotubes 4 and I0, the connections being made through resistors 5 and IIrespectively. The anode and cathode of tube 4 are interconnected througha time constant circuit comprising a capacitor 1 in series with aresistor 8. The junction between elements I and 8 "is connected to thegrid of tube ID. The anode of tube It is connected through a resistor 6.t the grid of tube 4.

The circuit arrangement as hereinabove de= scribed might be looked uponasv closely related to a multivibrator circuit- It does not, however,operate in the manner of a conventional multivibrator. It is asymmetricin operation and may be referred toas a flip-flop or univibratorcircuit. The operation may be better explained as follows:

To start oscillations, switch 23 is momentarily closed for the purposeof rendering tube 4 conductive. Normally this tube would stand in anon-conductive state by virtue of the voltage drop through resistor 9due to the normally conductive state in tube l0. Resistor 9, aspreviously stated, is chosen to have a relatively high ohmic valueprimarily for the purpose of holding tube 4 non-conductive, particularlyuntil oscillations are to be generated.

Upon closin the switch 23 the bias on tube 4 is reduced to such anextent that tube 4 starts to conduct. The coupling between the anode oftube 4 and the grid of tube l0 causes tube ID to be biased to cut-off inresponse to the conductive state invtube 4. This condition persistsWhile condenser 1 discharges through resistor 8, thus holding triode l 0non-conductive. When condenser E discharges sufficiently, the grid oftriode Ii] rises above the cut-off value and the initial states ofconduction and nonconduction in the respective tubes are restored. Thiscompletes the first cycle of the relaxation oscillator and the secondcycle starts as soon as con: denser l recharges through resistor 5. Thetriodes will continue to oscillate at a frequency dependent mostly onthe values of resistors 5, 8 and 9 and. condenser 1. I v

If coil I and condenser 2 are of such values as to resonate atapproximately the same frequency as the relaxation oscillations thenthis sine-wave tank circuit will be excited by the pulses of energy fedto it from the anode of triode In by way of resistor 6. As the sine-waveoscillations build up in the tank circuit comprising coil I andcondenser 2, the relaxation oscillations in triodes 4 and I!) willbecome completely synchronized to the natural frequency of said tankcircuit, since the latter will conmore especially that of Fig. 1. Line25 is the sine-wave voltage developed by the oscillator anddeliverable'across the terminals 30. Lines 26 and 21 are wave formsappearing on the anodes of the triodes 4 and I9 respectively. Thevertical portions of these waves forms indicate instants of triggering.The upper portions of the wave form 26 indicate the times when triode 4is completely out 01f and is non-conducting and the lower portions ofthis wave form indicate the conducting periods of triode 4. Wave form 21applies similarly to the triode I 0.

state and tube [0 toward a conducting state for v H the stable portionof each cycle, whereas an unstable condition or active state exists whentube 4 is conducting and tube l0 non-conducting.

The stable state is terminated by tube 4 being triggered by the positiverise in voltage of the tank circuit I, 2. During the unstable or activestate a pulse of energy is supplied to the tank circuit; fromrthe anodeof tube ID. The tubes then flop back to the stable state to wait for thenext triggering. In this manner the sine-wave tank circuit of coil I andcondenser 2 directly control the pulses. of energywhich drive it.

The modification shown in Fig. 2 differs from that of Fig. 1 chiefly inrespect to the substitution of a piezo-electric device l2 for the tankcir cuit I, 2. In order to provide a conductive circuitbetween the gridof tube 4 and ground a resistor 3. is connected across the terminals ofthe. piezo-electric device. The mode of operation of the. oscillatorcircuit arrangement shown in Fig. 2 will be apparent from the foregoingdescription of operation of the circuit of Fig. 1. The output may betaken oiI at. any suitable point, the same as in'Fig. 1, although outputterminals are not shown in- Fig. 2. The adjustable resistor 9 may bemanually controlled if desired to reduce its ohmic value for purposes ofstarting. Otherwise, the same starting switch 23 in series with a resstor 24 may be included in the circuit of Fig. 2 if desired.

Referring to Fig. 3, the modification therein shown is also similar tothe embodiment shown in Fig. l, but in this case the tubes 1 I and I8are. associated more in accordance with the arrangement of aconventional multivibrator. It will be noted that the anode of tube 18is coupled to the grid of tube I? through a capacitor I5. Also the anodeof tube I! is coupled to thegrid of tube I8 through a .capacitorlS. Thecathodes of the two tubes l! and I8 are directly grounded, so that it isnecessary to supply grid resistors l9 and 2D for the two tubesrespectively. Anode potential is supplied to the two tubes throughresistors l3 and I4.

In the circuit of Fig. 3 the grid of tube I1 is connected to groundthrough a resistor 29 in series with an inductive element 2! and thelatter is in shunt with a capacitor 22. The elements 2| and 22 form atank circuit which is used for stabilizing the frequency of oscillationsof the multivibrator.

In the operation of the circuit arrangement Referring now to Fig. 4, Ishow therein a series of wave forms which illustrate the characteristicsof the wave energy to be obtained at various points of the severalcircuit arrangements,

Wave forms 28 and 29 are those which would be observed at the anodes ofthe triodes 4 and I0 respectively when the flip-flop part of the circuitis operated at half the frequency of the tank circuit l, 2.

In this case it can be seen that tubes 4' and I9 are triggered onalternate cycles of the sine wave output from the tank circuit. Theoutput for this type of operation remains the same as shownin line 25.sub-harmonic operation is obtained by readjustment of the values ofresistors 8 and 9.

It will be apparent to those skilled in the art that the relaxationoscillator of my invention is capable of modification in various ways tomeet the particular requirements of associated circuits. The output fromthe oscillator may be taken oil a't'various points. The circuitsthemselves are also capable of modification in various ways withoutdeparting from the spirit and scope of the invention.

I claim:

1. A frequency stable sine wave generator including anelectron dischargenetwork comprising a first electron discharge device having cathode,grid and anode electrodes, a second electron discharge device havingcathode, grid. and anode electrodes, load resistors connected to theanode electrodes of said electron'discharge devices, a capacitorintercoupling the anode electrode of said first electron dischargedevice and the grid of said second electron discharge device, a gridresistor connecting the grid electrode of said second electron dischargedevice to the cathode electrodes of both of said electron dischargedevices, a further resistor connected between said cathode electrodesand ground, and means to connect the positive pole of a source of directpotential to said load resistors and to connect the negative pole ofsaid source to ground, said further resistor having a value normally atwhich said second discharge device is conducting and said firstdischarge device is blocked due to current flow of said conductingsecond discharge device, a switch and resistance element adapted to beconnected across said further resistor effective to reduce the value ofsaid further resistor to reduce the bias on the grid electrode of saidfirst electron discharge device to render the same conducting and blocksaid second electron discharge device after which said second electrondischarge device becomes conducting efiectively to restore said networkto said normal condition, a resonant circuit comprising an inductor anda capacitor connected in parallel between the grid electrode of saidfirst electron discharge device and ground, and a second resistorconnecting the anode of said second electron discharge device to thegrid of said resonant circuit connected to the grid electrode of saidfirst electron discharge device to sustain oscillations at the resonantfrequency of said resonant circuit. 7

2. A frequency stable sine wave generator including an electrondischarge network compris- This 5 ing a first electron discharge devicehaving cathode, grid and anode electrodes, a second electrcn dischargedevice having cathode, grid and anode electrodes, load resistorsconnected to the anode electrodes of said electron discharge devices, acapacitor intercoupling the anode electrode of said first electrondischarge device and the grid of said second electron discharge device,a grid resistor connecting the grid electrode of said second electrondischarge device to the cathode electrodes of both of said electrondischarge devices, a further resistor connected between said cathodeelectrodes and the grid electrode of said first electron dischargedevice, means connecting the grid electrode of said first electrondischarge device to ground with respect to direct current, and means toconnect the positive pole of a source of direct potential to said loadresistors and to connect the negative pole of said source to ground,said further resistor having a value normally at which said seconddischarge device is conducting and said first discharge device isblocked due to current fiow of said conducting second discharge device,means to reduce the value of said further resistor to reduce the bias onthe grid electrode of said first electron discharge device to render thesame conducting and block said second electron discharge device afterwhich said second electron discharge device becomes conductingeffectively to restore said electron discharge network to said normalstate, a resonant circuit element interposed between the grid electrodeof said first electron discharge device and ground, and a secondresistor connecting the anode of said second electron discharge deviceto the grid electrode of said first electron discharge device to sustainoscillations at the resonant frequency of said resonant circuit element.

3. A frequency stable sine wave generator including an electrondischarge network comprising a first electron discharge device havingcathode, grid and anode electrodes, a second electron discharge devicehaving cathode, grid and anode electrodes, load resistors connected tothe anode electrodes of said electron discharge devices, a capacitorinter-coupling the anode electrode of said first electron dischargedevice and the grid of said second electron discharge device, a gridresistor connecting the grid electrode of said second electron dischargedevice to the cathode electrodes of both of said electron dischargedevices, a further resistor connected between said cathode electrodesand ground, a second grid resistor connected between the grid electrodeof said first electron discharge device and ground, and means to connectthe positive pole of a source of direct potential to load resistors, andto connect the negative pole of said source to ground, said furtherresistor having a value normally at which said second discharge deviceis conducting and said first discharge device is blocked due to currentflow of said conducting second discharge device, means effective toreduce the value of said further resistor to reduce the bias on the gridelectrode of said first electron discharge device to render the sameconducting and block said second electron discharge device after whichsaid second electron discharge device becomes conducting efiectively torestore said electron discharge network to said normal state, apiezoelectric crystal connected between the grid electrode of said firstelectron discharge device and ground and a second resistor connectingthe anode of said second electron discharge device to the grid electrodeof said first electron discharge device 6 to sustain oscillations at thenatural frequency of said piezoelectric crystal.

4. A frequency stable periodic wave generator including an electrondischarge network comprising an electron discharge device havingcathode, grid and anode electrodes, a load element coupled to the anodeelectrode of said electron discharge device, a resistor connectedbetween the grid and cathode electrodes of said electron dischargedevice, a further resistor connected to the cathode electrode of saidelectron discharge device, means to apply direct potential to said loadelement and said further resistor to produce current fiow therein andpotential drops across said load and said further resistors, a furtherelectron discharge device having a cathode connected to the cathode ofthe first said electron discharge device, an anode to which saidpotential is applied through the intermediary of an output element and agrid coupled to the terminal of said further resistor remote from thecathodes of said electron discharge devices, said further resistorhaving a value at which the potential drop thereat renders said furtherelectron discharge device non-conducting, a capacitor coupling the anodeof said further electron discharge device to the grid electrode of thefirst said electron discharge device, an impedance element coupledbetween the anode of the first said electron discharge device and thegrid of said second electron discharge device, means to reduce theresistance of said further resistor to render said further electrondischarge device conducting to charge said capacitor and thereby applycut-off potential to the grid electrode of the first said electrondischarge device, the first said electron discharge device againconducting upon dissipation of the charge on said capacitor through thefirst said resistor to block said further electron discharge device, andmeans periodically rendering said further electron discharge deviceconducting, said means comprising a resonant circuit interposed betweenthe grid of said further electron discharge device and the cathodes ofsaid electron discharge devices.

5. A frequency stable periodic wave generator including an electrondischarge network comprising a first electron discharge device havingcathode, grid and anode electrodes, a second electron discharge devicehaving cathode, grid and anode electrodes, load elements connected tothe anode electrodes of said electron discharge devices, a capacitorintercoupling the anode electrode of said first electron dischargedevice and the grid of said second electron discharge device, a resistorconnecting the grid electrode of said second electron discharge deviceto the oathode electrodes of both of said electron discharge devices, afurther resistor connected between said cathode electrodes and a pointof fixed reference potential, an element coupling the grid electrode ofsaid first electron discharge device to said point of fixed referencepotential with respect to direct current, and means to apply positivedirect potential to said electron discharge network between said pointof fixed reference potential and load elements, said further resistorhaving a value normally at which said second discharge device isrendered conducting and said first discharge device is blocked due tocurrent flow of said conducting second discharge device, means to removethe bias on the grid electrode of said first electron discharge deviceto render the same conducting and block said second electron dischargedevice after which said discharge network is re- 7 8 stored to saidnormal condition to complete one V UNITED STATES PATENTS cycle ofoscillation only, and a resonant circuit Number Name Date interposed inthe'grid electrode circuit of s i 2 053 7 w n S t'g 1936 first electrondischarge device to reduce said bia 7 47 Braaten 1937 periodically atthe resonant frequency of sai 5 2132555 Geiger pm 3 resonant circuit tosustain said oscillations. 2,395,363 B1111 1 2,406,096 Morrison Aug. 20,1946 WARREN BLISS- 2,411,598 Smith Nov. 26, 1946 2,419,772 Gottier Apr.29, 1947 7 REFERENCES CITED FOREIGN PATENTS fiIeTh)?iggoiggiinzeferences are of record 1n the Number Counfiry- 7 Date485,934 Great Britain May 26, 1938

